The present disclosure relates to a voltage-mode transmitter equalizer (TxEQ).
A transmitter passes output signals to a receiver over a channel or signal path such as one or more transmission lines. The transmitter may include equalization to pre-compensate for data-dependent distortion in the signal as it propagates along the transmission line. A transmitter including equalization is often called a “transmitter equalizer” or an “equalizing transmitter.”
Transmitters can be classified as current mode or voltage mode. Current mode transmitters typically have separate devices for controlling the output signals and for providing impedance matching with the impedance of the transmission line(s). Thus, it is easier to control these factors in current mode transmitters. In a current-mode transmitter equalizer, an output stage of the transmitter is driven by logic that computes an appropriate output signal level (i.e., output voltage) for each bit of data to be transmitted, depending upon a data pattern formed by a sequence of digital values (data bits) to be transmitted by the transmitter, including a current data bit to be transmitted and any number of previous and/or possibly post data bits that have and/or will be transmitted. With separate devices for controlling the output level and for providing impedance matching with the impedance of the transmission line, it is relatively straightforward for a current-mode transmitter equalizer to control these factors. Conventional current mode transmitters, however, are not particularly efficient because they normally extract a power supply current that is four times the signaling current delivered to the transmission line(s).
A voltage-mode transmitter generates an output voltage that is controlled to produce a net voltage swing across a load resistance corresponding to an input signal. In contrast to current-mode transmitters, voltage-mode transmitters are able to deliver the entire power supply current to a transmission line because a single mechanism or circuit component is typically used to control both the output signal level and to provide impedance matching.